Bobbin thread feeder of sewing machine

ABSTRACT

The present invention provides a bobbin thread feeder of sewing machine of simple structure in which a lower thread can be reliably fed at an appropriate tension. A lower thread bobbin  21  can be removably contained through an opening for containing a lower thread bobbin  17  in a rotary hook  20  of a horizontal rotary hook  30  provided in a sewing machine frame. A thread tension plate and a thread tension spring are attached while overlapping along the inner circumference of the rotary hook  20,  and function as a tension generating portion  22  for imparting resistance to pulling out a lower thread being guided through the gap between the thread tension plate and the thread tension spring. A needle plate  16  with an opening for taking the lower thread bobbin  21  in and out is provided above the rotary hook  20.  The needle plate  16  comprises a guiding slit  27  that guides the lower thread formed thereon. The guiding slit  27  is formed substantially linearly in the extending direction of the overlapping portion of the thread tension plate and the thread tension spring.

TECHNICAL FIELD

The present invention relates to a bobbin thread feeder of sewing machine comprising a horizontal rotary hook that removably contains a lower thread bobbin, wherein a lower thread can be easily set during a sewing operation.

BACKGROUND ART

As sewing machines for household use, a model comprising a horizontal rotary hook in which a lower thread bobbin does not have to be contained in a bobbin case when being attached is becoming a mainstream instead of the one comprising a vertical rotary hook. In the case of sewing machines comprising a horizontal rotary hook, the lower thread bobbin need only to be set through an opening above the horizontal rotary hook into a rotary hook, and thus a bobbin thread feeder is provided so that a lower thread can be reliably fed.

For example, in Patent Document 1, a bobbin thread feeder is consisted such that a containing portion of a rotary hook in the shape of a cylindrical container is positioned below an opening for containing a lower thread bobbin provided at a needle plate. The lower thread bobbin is contained when a user directly sets the lower thread bobbin from above through the opening for containing the lower thread bobbin into the rotary hook. Accordingly, the lower thread bobbin does not have to be contained in a bobbin case when being set into the rotary hook as in the case of using a vertical rotary hook, and thus an operation that sets the lower thread bobbin can be easily performed.

The bobbin thread feeder comprises a tension generating portion in order to impart a resistance to a lower thread being pulled out which is guided from the lower thread bobbin. The tension generating portion is attached to a recessed portion formed along part of the inner circumferential face of the containing portion of the rotary hook, in a state where a thread tension plate and a thread tension spring are overlapped. The user sets the lower thread bobbin as described above, and then performs an operation to put a lower thread pulled out of the lower thread bobbin through the tension generating portion. In the case where the sewing machine is operated in a state where the lower thread is not properly put through the tension generating portion, the feeding amount of the lower thread becomes excessive as the tension of the lower thread decreases, the balance with the upper thread is lost, and thus the sewing operation cannot be performed well.

Thus, in Patent Document 1, a plate-shaped guide member disposed substantially in the horizontal direction above the tension generating portion of the rotary hook is provided so that a lower thread pulled out of the lower thread bobbin is guided to the tension generating portion. When the lower thread pulled out is moved so as to be guided by the guide member provided above the tension generating portion, the lower thread is reliably guided to between the thread tension plate and the thread tension spring and to the tension generating portion. Accordingly, the user can set a lower thread by a simple operation that guides the lower thread pulled out of the lower thread bobbin with the guide member.

Furthermore, in Patent Document 2, the front edge portion and the side edge portion of a needle plate are used as slits that guide a lower thread, and a connection slit that connects an opening for containing a lower thread bobbin and the front edge portion of the needle plate is formed in the front portion of the needle plate. When the user winds the lower thread from the connection slit to the front edge portion and the side edge portion of the needle plate, the lower thread is guided to between the thread tension plate and the thread tension spring and to the tension generating portion. Accordingly, the user can set a lower thread by a simple operation that guides the lower thread pulled out of the lower thread bobbin along the circumferential edge of the needle plate.

Patent Document 1: JP H10-146489A Patent Document 2: JP 2005-312733A DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, in Patent Document 1, there is a problem in that the structure of the bobbin thread feeder becomes complex because a guide member has to be additionally comprised only in order to guide a lower thread. Furthermore, in Patent Document 2, although a guide member does not have to be additionally provided, the needle plate has to be processed into an appropriate shape according to the shape and the position of the lower thread bobbin. Accordingly, in both cases, it is difficult to reduce the production costs. A simpler structure is required for sewing machines for household use, which are strongly required to be competitive in price.

The present invention was made in view of these circumstances, and it is an object thereof to provide a bobbin thread feeder of sewing machine that can reliably feed a lower thread at a proper tension, and that has a simple structure.

Means for Solving Problem

In order to achieve the above-described object, a first aspect of the present invention is directed to a bobbin thread feeder of sewing machine, in which a lower thread bobbin can be removably contained through an opening for containing the lower thread bobbin in a rotary hook of a horizontal rotary hook provided in a sewing machine frame, and in which a tension generating portion is provided for imparting a resistance to a lower thread being pulled out while passing and being guided between a thread tension plate and a thread tension spring, which are attached while overlapping along the inner circumference of the rotary hook, wherein a needle plate with an opening for taking the lower thread bobbin in and out is provided above the rotary hook, the needle plate comprises a guiding slit for guiding the lower thread, and the guiding slit is formed substantially linearly in the extending direction of the overlapping portion of the thread tension plate and the thread tension spring.

According to the first aspect of the present invention, a lower thread bobbin can be removably contained through an opening for containing the lower thread bobbin in a rotary hook of a horizontal rotary hook provided in a sewing machine frame. A thread tension plate and a thread tension spring are attached while overlapping along the inner circumference of the rotary hook, and function as a tension generating portion that imparts a resistance to a lower thread being pulled out while passing and being guided between the thread tension plate and the thread tension spring. A needle plate with an opening for taking the lower thread bobbin in and out is provided above the rotary hook. A guiding slit for guiding the lower thread is formed on the needle plate. The guiding slit is formed substantially linearly in the extending direction of the overlapping portion of the thread tension plate and the thread tension spring. When a user moves the lower thread along the guiding slit on the upper face side of the rotary hook that contains the lower thread bobbin, the lower thread can be guided to the overlapping portion of the thread tension plate and the thread tension spring, and an appropriate tension is imparted to the lower thread. Accordingly, it is possible to provide a bobbin thread feeder that does not impair the function of feeding the lower thread by imparting an appropriate tension thereto even if a guide member is not additionally provided, only by a simple production process that forms a substantially linear slit on the needle plate. Thus, production costs can be reduced.

Furthermore, a second aspect of the present invention is directed to the bobbin thread feeder of sewing machine according to the first aspect, wherein the needle plate comprises a thread-cutting portion for cutting the lower thread at a predetermined position where the length of the lower thread pulled out of the lower thread bobbin is longer than the length to the end of the guiding slit.

According to the second aspect of the present invention, the bobbin thread feeder comprises a thread-cutting portion for cutting the lower thread at a predetermined position of the needle plate such that the length of the lower thread pulled out of the lower thread bobbin is longer than the length to the end of the guiding slit. In the case where the length of the lower thread pulled out of the lower thread bobbin is too long, the lower thread pulled out with a blade point of an outer rotary hook and the upper thread may be intricately intertwined with each other. Furthermore, in the case where the length of the lower thread pulled out is too short, the blade point of the outer rotary hook may fail to catch the lower thread. Thus, when the lower thread can be reliably cut into an appropriate length, the user can easily set the lower thread.

EFFECT OF THE INVENTION

According to the present invention, when the user moves the lower thread along the guiding slit on the upper face side of the rotary hook that contains the lower thread bobbin, the lower thread can be guided to the overlapping portion of the thread tension plate and the thread tension spring, and an appropriate tension is imparted to the lower thread. Accordingly, it is possible to provide a bobbin thread feeder of sewing machine that does not impair the function of feeding the lower thread by imparting an appropriate tension thereto even if a guide member is not additionally provided, only by a simple production process that forms a substantially linear guiding slit on the needle plate. Thus, production costs can be reduced because the number of parts is not increased.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing the appearance of a sewing machine according to an embodiment of the present invention.

FIG. 2 is a plan view of a needle plate according to the embodiment of the present invention.

FIG. 3 is a plan view showing the configuration of a bobbin thread feeder according to the embodiment of the present invention.

FIG. 4 is a perspective view showing the configuration of an rotary hook according to the embodiment of the present invention.

FIG. 5 is a front view of a thread tension plate according to the embodiment of the present invention.

DESCRIPTION OF NUMERALS

-   11 Sewing machine frame -   16 Needle plate -   17 Opening for containing a lower thread bobbin -   20 Rotary hook -   21 Lower thread bobbin -   22 Tension generating portion -   23 Thread tension plate -   24 Thread tension spring -   27 Guiding slit -   28 Thread-cutting portion -   29 Outer rotary hook -   30 Horizontal rotary hook

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, “front”, “rear”, “left” and “right” refer to the front, rear, left and right directions viewed by an operator operating a sewing machine. FIG. 1 is a perspective view showing the appearance of a sewing machine according to an embodiment of the present invention. As shown in FIG. 1, the sewing machine according to the embodiment comprises a sewing table 12 configured as part of a sewing machine frame 11, and an arm portion 13 integrated with the sewing machine frame 11 and provided above the sewing table 12. A needle bar 15 to which a sewing needle 14 is fixed is provided at the lower front portion of the arm portion 13, and a sewing operation is performed when a well known drive mechanism (not shown) vertically moves the needle bar 15.

On a portion that opposes the needle bar 15 and in which the sewing operation is performed, a needle plate 16 made of metal is provided. FIG. 2 is a plan view of the needle plate 16 according to the embodiment of the present invention. A needle hole 16 a through which the sewing needle 14 passes is formed on the needle plate 16, and an opening for containing the lower thread bobbin 17 which opens in a rectangular shape is formed in front of the needle hole 16 a. In ordinary use, a transparent cover 18 (FIG. 1) is placed on the opening for containing the lower thread bobbin 17. Below the needle plate 16 in the sewing machine frame 11, a feed dog mechanism (not shown) for feeding fabric that is driven according to the vertical movement of the needle bar 15 is provided, and a bobbin thread feeder according to this embodiment is also provided.

FIG. 3 is a plan view showing the configuration of the bobbin thread feeder according to the embodiment of the present invention. FIG. 3 shows a plan view from above in a state where the cover 18 is removed and the opening for containing the lower thread bobbin 17 is open. The bobbin thread feeder according to this embodiment is configured to dispose a horizontal rotary hook 30 below the needle plate 16. The horizontal rotary hook 30 is configured with an outer rotary hook 29 that horizontally rotates in synchronization with the vertical movement of the needle bar 15, and with a rotary hook 20 that is contained in the outer rotary hook 29 and provided not to rotate in synchronization with the outer rotary hook 29. The outer rotary hook 29 has a blade point (not shown) that catches a lower thread, and forms stitches by intertwining an upper thread with a lower thread according to the vertical movement of the needle bar 15.

FIG. 4 is a perspective view showing the configuration of the rotary hook 20 according to the embodiment of the present invention. As shown in FIG. 4, the rotary hook 20 is substantially in the shape of a cylindrical container, and has a containing portion 20 a that can contain a lower thread bobbin 21 below the opening for containing the lower thread bobbin 17. The lower thread bobbin 21 is removably set through the opening for containing the lower thread bobbin 17 into the containing portion 20 a. Furthermore, a recessed portion (hooked by a finger) 20 c for detaching the contained lower thread bobbin 21 is provided on the outer circumferential portion of the containing portion 20 a.

The rotary hook 20 is provided with a tension generating portion 22. The tension generating portion 22 is attached with screws 25 and 26 or the like to an arc-shaped recessed portion 20 d formed on part of the inner circumferential face of the containing portion 20 a of the rotary hook 20, in a state where a thread tension plate 23 and a thread tension spring 24 are overlapped. The thread tension plate 23 and the thread tension spring 24 are arc in shape respectively along the recessed portion 20 d in the same way, and a overlapping portion of the thread tension plate 23 and the thread tension spring 24 is set into the arc-shaped recessed portion 20 d on the inner circumferential face of the containing portion 20 a of the rotary hook 20.

FIG. 5 is a front view of the thread tension plate 23 according to the embodiment of the present invention. As shown in FIG. 5, the thread tension plate 23 where a hole 23 a is formed in the lower left portion comprises a slit 23 b formed thereto that is a cutout, extending from substantially the central portion of the upper edge to diagonally the lower left to reach the hole 23 a. Furthermore, a groove portion 23 c for stably pulling the lower thread guided to the hole 23 a out of the needle hole 16 a of the needle plate 16 is provided near the hole 23 a on the left of the upper edge.

The thread tension spring 24 is provided with a step portion 24 a at the right end portion. The thread tension plate 23 and the thread tension spring 24 have a slight gap therebetween at substantially the central portion (a portion near the leading end of the slit 23 b), and are substantially in close contact with each other at the left end portion (a portion near the hole 23 a).

With this configuration, the lower thread pulled out of the lower thread bobbin 21 is guided along the slit 23 b to the hole 23 a. Accordingly, a resistance is imparted to the lower thread by the power of the thread tension plate 23 and the thread tension spring 24 pressing the lower thread therebetween, and the lower thread is fed in a state where an appropriate tension is imparted thereto.

In this embodiment, as shown in FIGS. 2 and 3, the needle plate 16 is provided with a substantially linear guiding slit 27. The angle of the guiding slit 27 substantially coincides with the direction circumscribing the lower thread bobbin 21, that is, the direction in which the lower thread is pulled out.

More specifically, the guiding slit 27 is provided in the extending direction of the thread tension plate 23 and the thread tension spring 24 provided in the shape of arc on the inner circumferential face of the rotary hook 20 toward the main unit. Thus, the lower thread is passed between the thread tension plate 23 and the thread tension spring 24 and an appropriate tension is imparted to the lower thread when the user simply guides the lower thread along the guiding slit 27, without being conscious of guiding the lower thread to the groove portion 23 c above the thread tension plate 23.

Furthermore, the needle plate 16 is provided with a thread-cutting portion 28. The thread-cutting portion 28 is configured with a closed-bottom groove 28 a that is formed from the end of the guiding slit 27 along the outer edge of the needle plate 16, and a chamfering portion for a cutter 28 c that guides a lower thread to the cutter 28 b at a position where a sufficient length of the lower thread can be secured.

In the case where a sewing machine comprising the bobbin thread feeder configured as described above is used, the user first removes the cover 18 of the sewing table 12, and fits and sets the lower thread bobbin 21 into the containing portion 20 a of the rotary hook 20. Then, the lower thread is pulled out of the lower thread bobbin 21, and caught on the slit 23 b of the thread tension plate 23 first.

Next, the lower thread is rotated clockwise in a state where the lower thread is caught on the slit 23 b, and guided toward the guiding slit 27 of the needle plate 16. When the lower thread is guided along the direction of the guiding slit 27, the lower thread caught on the slit 23 b is lowered along the slit 23 b, and guided to the hole 23 a.

When the lower thread is guided to the hole 23 a, the lower thread is brought into a state where an appropriate tension is imparted by the power pressed between the thread tension plate 23 and the thread tension spring 24. The user pulls out the lower thread along the guiding slit 27 in a state where a tension is imparted to the lower thread.

At the end portion of the guiding slit 27, the lower thread is guided to the closed-bottom groove 28 a of the needle plate 16, and thus, the lower thread is guided from the end portion of the guiding slit 27 to the cutter 28 b, along the closed-bottom groove 28 a formed along the outer edge of the needle plate 16. When the lower thread penetrates in the chamfering portion for the cutter 28 c, the lower thread is cut with the cutter 28 b.

In this state, the user vertically moves the needle bar 15 with a drive mechanism (not shown). When the needle bar 15 is vertically moved, the outer rotary hook 29 of the horizontal rotary hook 30 rotates horizontally, and the upper thread is intertwined with the lower thread caught on the blade point, and pulled upward out of the needle hole 16 a of the needle plate 16. In this state, the lower thread is pulled out of the hole 23 a of the thread tension plate 23 of the rotary hook 20 through the groove portion 23 c to the needle hole 16 a, and thus, the user does not have to be conscious of guiding the lower thread to the groove portion 23 c. When the upper thread and the lower thread pulled out are untwined, it is ready for sewing.

In this embodiment, the length of the lower thread pulled out can be kept substantially constant. Accordingly, there is no possibility that the lower thread pulled out at the blade point of the outer rotary hook 29 is intricately intertwined with the upper thread, for example, as in the case where the lower thread pulled out of the lower thread bobbin 21 is too long. Furthermore, there is no possibility that the blade point of the outer rotary hook 29 fails to catch the lower thread, for example, as in the case where the pulled out lower thread is too short, and thus, the user can reliably prepare for sewing.

Thus, according to this embodiment, the lower thread is guided between the thread tension plate 23 and the thread tension spring 24 to pass through the tension generating portion 22 only by the operation in which the lower thread pulled out of the lower thread bobbin 21 is rotated clockwise in a state where the lower thread is caught on the slit 23 b on the upper face side of the rotary hook 20 and moved along the guiding slit 27 of the needle plate 16. Accordingly, without additionally providing an arched guide member or the like, for example, the lower thread can be reliably set. Furthermore, the guiding slit 27 is substantially linear, and thus, the minimum working process will do. Accordingly, production costs can be reduced.

Moreover, in this embodiment, the needle plate 16 is provided with the thread-cutting portion 28, and thus, the length of the lower thread pulled out of the lower thread bobbin 21 can be substantially constant in length. Accordingly, harmful effect of the pullout length can be prevented in advance.

It should be appreciated that the present invention can be worked with various modifications made to the above-described embodiment without departing from the gist of the invention, for example, mainor change in the configuration of the tension generating portion 22, change in the shape of the thread tension plate 23, change in the position to attach the thread-cutting portion 28, or the like. 

1. A bobbin thread feeder of sewing machine, in which a lower thread bobbin can be removably contained through an opening for containing the lower thread bobbin in a rotary hook of a horizontal rotary hook provided in a sewing machine frame, and in which a tension generating portion is provided for imparting a resistance to a lower thread being pulled out while passing and being guided between a thread tension plate and a thread tension spring, which are attached while overlapping along the inner circumference of the rotary hook, wherein a needle plate with an opening for taking the lower thread bobbin in and out is provided above the rotary hook, the needle plate has a thread-cutting portion for cutting the lower thread, and a guiding slit for guiding the lower thread to a position near the thread-cutting portion, and the guiding slit is formed toward the side away from a user substantially linear in a direction for circumscribing the inner circumference of the rotary hook at a portion where the lower thread is pulled out of the tension-generating portion.
 2. The bobbin thread feeder of sewing machine according to claim 1, wherein a lower side of an edge on the side of a needle hole of the guiding slit on the needle plate is chamfered. 